Refrigerated dispensing appliances (including vending machines and reach-in type beverage coolers) provide for cost-effective delivery of consumer items. In principle, they provide full-time product availability with minimal intervention by a human operator. However, full-time operation can result in wasted energy consumption as the machine may be on for long intervals of inactivity. The concern for energy consumption is especially acute in the case of refrigerated dispensing appliances.
Refrigerated dispensing appliances generally maintain their contents at a standard temperature on the order of 36° F. There can be various reasons for keeping the dispensable items cold. Cold generally helps preserve perishable food items. In some cases, for example, with soda and other beverages, the items may taste better chilled.
Typically, the dispensable items are maintained within a chamber that is thermally insulated from the exterior of the machine. A cooling system withdraws heat from the chamber. The cooling system can include an evaporator, a compressor, a condenser, and a metering (flow constricting) device.
When the cooling system is on, coolant liquid, e.g., Freon, enters the evaporator. The evaporator is thermally coupled to the refrigerated chamber. The coolant liquid is generally colder than the chamber so that the coolant removes heat from the chamber. The liquid evaporates as it absorbs the heat. The evaporated coolant is pumped out of the evaporator through a suction line by a compressor. The compressor increases the pressure of the coolant, raising its temperature in the process. The pressurized coolant is then directed to a condenser via a discharge line. The condenser couples the coolant to a chilled environment. This causes the coolant to give up heat and condense into a liquid. The liquid flows through a liquid line, including the flow meter (which is basically a flow restriction) back to the evaporator to begin another cooling cycle. The evaporator removes heat from the nearby chamber air. To ensure that the cool air reaches the dispensable items and to ensure a uniform temperature within the chamber, the chamber air is circulated. Generally, one or more fans are operated within the chamber interior to effect this circulation.
One or more temperature sensors monitor the temperature inside the chamber. Typically, there is a desired temperature range for the vended items, for example, 0° to 2° C. (˜32° F. to 36° F.) for cold drinks. When the chamber temperature reaches the higher threshold, the compressor is activated and the cooling process begins. When the chamber temperature falls to the lower threshold, the compressor is turned off, and cooling effectively halts. Another cooling cycle can begin when the temperature reaches the upper threshold due to inevitable heat transfer through the chamber wall.
Refrigerated dispensing appliances consume considerable electric power. Typically, most of the power consumed by a refrigerated dispensing appliance is consumed by the cooling system, and especially by the compressor, even though it is not operated continuously. However, the fans, the dispensing mechanism, the money handling mechanisms, panel lights, sensors, and control electronics all consume power. For reasons of energy conservation and cost, it is desirable to be able to reduce the energy consumed by a refrigerated dispensing appliance without adversely affecting its service (to patrons) and its economic viability (to the appliance owner).
The most straightforward approach to saving energy is to disconnect AC power. For example, a refrigerated vending appliance could be turned off during non-business hours, e.g., from 10 pm to 6 am. To avoid the inconvenience of manual activation and inactivation, an external timer can be used to control AC power to the vending machine. However, whether power to the vending machine is switched by a human operator or a timer, potential patrons are denied dispensable items during off hours. Additionally, most artificially-sweetened products deteriorate under such temperature cycling. Such temperature cycling also causes cold cans and bottles to “sweat” or develop a water film due to condensation.
Additionally, present cold drink dispensing machines are nearly all electronically controlled, having internal electronics to control operation of the cooling and possibly lighting systems, as well as cash collection and disbursement and possibly non-cash transactions (e.g. credit cards). However, reach-in type beverage coolers, lacking the requirements for cash management, are typically mechanically based, using a simple mechanical thermostat to regulate the operation of its cooling system.
U.S. Pat. No. 6,243,626, to Schanin, commonly assigned to the assignee of the present invention, discloses an external power control system for a vending machine that includes an occupancy sensor. This can be used to ensure a vending machine is on whenever people are in its vicinity. An ambient thermo-sensor can also be included to determine a reactivation time to prevent the dispensable items from become unacceptably warm.
U.S. Pat. No. 6,389,822 to Schanin, commonly assigned to the assignee of the present invention, discloses a refrigerated soda vending machine that includes temperature sensors for monitoring temperature within its refrigerated chamber and temperature of the ambient air external to the chamber, and an occupancy sensor for monitoring occupancy in the vicinity of the chamber. The sensor data is used to determine when to switch between a normal-operation mode and a power-conservation mode of operation. In the normal mode of operation, fans circulate air within the chamber to maintain a relatively uniform temperature throughout the chamber. During power-conservation mode, the fans are off most of the time the compressor is off. In the absence of circulation, the temperature within the refrigerated chamber stratifies so that a lower cool zone and an upper warm zone can be differentiated. Cold drink cans or bottles are held in vertical stacks so that the lowest product is located in the cool zone. Product is dispensed from the bottom of the stacks and thus only from the cool zone. The machine automatically switches from the power-conserving mode to the normal mode in the event that the occupancy sensor senses occupancy in the vicinity of the machine. With this arrangement, a patron can obtain an optimally chilled product even though the average temperature in the chamber is above the optimal temperature range. Thus, energy can be conserved and operating costs reduced while meeting patron's expectations for cold beverages at all times.
While these power-saving control mechanisms are effective in that there is no risk of lost sale due to a customer believing the machine is non-operational, such mechanisms may be inefficient in circumstances where people walking in the vicinity of the machine are not interested in buying products. In such circumstances, exiting the power-conserving mode based on occupancy is not efficient.